Thiourea-hydrocarbon complexes



Patented Mar. 7, 1950 THIOUREA-HYDROCARBON COMPLEXES AND PROCESS FOR PREPARING SADIE Lloyd C. Fetterly, Long Beach, Calif., assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware No Drawing. Application February 21, 1947, Serial No. 730,182

16 Claims.

This invention relates to new hydrocarbon complexes, and more particularly pertains to complexes of hydrocarbons and thiourea, as well as to the method of forming them.

Problems which are always present when dealing with hydrocarbons are their separation, purification and recovery. This is true especially with petroleum, where a complicated mixture of hydrocarbons is always present in the crude product and in its various fractions. Crude petroleum and petroleum products usually contain normal parafiins, isoparafiins, olefines, naphthenes and/or aromatics. The variety and complexity of these mixtures usually is complicated during refining and alteration processes, such as b distilling, acid treating, isomerizing, alkylating, cracking, hydroforming, polymerizing, etc. Processes such as these are utilized to produce desired mixtures of hydrocarbons for specific purposes. However, during any of the various treatments to which such mixtures are improvements have been proposed over a long period for processes to obtain high yields of desired fractions, to obtain more highly purified individual hydrocarbons, etc.

Other industries than the petroleum industry experience similar problems. For example, difficulties have been experienced in isolating specific terpene hydrocarbons from the m xture of materials normally present in pine oil and its derivatives. Similarly, the coal tar industry has always experienced difficulty in separating mixtures obtained by the destructive distillation of coal into its component parts.

Although a large number of specific improvements and new processes have been proposed for the solution of problems such as those above, as well as for similar problems, very few means have beenv discovered for satisfactory separation of specific hydrocarbons or types of hydrocarbons from mixtures thereof. Moreover, even those few methods which have shown promise technically have for the most partbeen impractical from a commercial standpoint because of the adverse economics involved.

Distillation has heretofore been the chief means utilized for the separation, concentration and or isolation and purification of hydrocarbons from mixtures containing them. However, a few laboratory methods have been proposed for the preparation of crystalline complexes of certain hydrocarbons and for the separation of one type of hydrocarbon from another.

2 Also, Barrer (U. S. Patent 2,306,610) has proposed the use of a zeolite as a molecular sieve. Sachanen (Chemical Constituents of Petroleum, page 187 (1945)) has taught the use of chlorosulfonic acid for the formation of complexes with tertiary hydrocarbons and the use of antimony pentachloride for the same purpose. Extractive distillation has been utilized, according to Griswald and Van Berg (Ind. Eng. Chem.

38, l77 (1946)), and solvent extraction has been described by Anderson (U. S. Patent 2,389,176). The conclusions reached and the aims achieved in most of these cases have been substantially on an empirical basis, and the use of any of them for the large-scale fixation, isolation or concentration of specific hydrocarbons has not been technically satisfactory or economically feasible.

It is well known that high octane gasolines are improved by the removal of normal hydrocarbons, but this is often difiicult or expensive to achieve, due to the similar boiling points of certain fractions having high octane numbers, and other fractions associated therewith which have low octane ratings. At the present time complicated processes are required for the isolation of high octane fractions which can be used for blending purposes. An methods which could be devised to achieve the isolation of high octane fractions, or to remove low octane material from cuts rich in high octane material would be of immediate value to the petroleum industry.

Likewise, the production of Diesel engine fuels involves the isolation of fuel oils having high octane numbers and Diesel indices, empirical ratings directly related to the type and quantity of certain hydrocarbon fractions present therein. A process capable of isolating preferred fractions from low grade stocks would be of substantial value in improving Diesel fuel production.

In specialty products, such as medicinals', household sprays, and hydrocarbons for many chemical purposes, it is highly desirable and at times essential to be able to use hydrocarbons having substantially no color. The decolorization of hydrocarbons generally involves a series of steps involving complicated apparatus, excessive labor costs and extended processing time. Any method which was relatively simple and which would effect decolorizing to the desired degree would be of value to the petroleum, naval stores and coal tar industries.

The presence of certain sulfur compounds, es-

pecially in petroleum fractions obtained from 3 crudes having a high sulfur content, has neces sitated the use of doctor treating and other more or less elaborate methods for the elimination of sulfur and sulfur-containing fractions, both for vthe reduction of objectional odor and-the improvement of corrosion characteristics of the finished product. Improved methods are required for the elimination of sulfur-bearing constituents of hydrocarbons, and for the concentration of high sulfur fractions for uses where the presence thereof is desirable or at least not objectionable.

Many hydrocarbon materials, and especially those store-d for long periods in contact with air or used where oxidation can rapidly or easily occur, show the undesirable feature of resinification or gum formation. This phenomenon is apparently due to oxidation of certain of the hydrocarbons, especially the olefins, when in contact with oxygen and various metals such as iron, copper, etc., or metal oxides, which appear to act as promoters for the gum formation. Many additives have been proposed, generally known as anti-oxidants for minimizin these effects. However, an inherent disadvantage of the use of such additives is that they usually cause engine lacquering when present in quantities sufficient to reduce gum formation. Therefore a simple method which could be used for removing gumforming fractions from hydrocarbon mixtures would find immediate utilization, especially in the petroleum industry.

Another problem which has been inadequately solved up to the present time is the removal of gum and resin bodies which have been formed by oxidation or other means. Such purification usually involves complicated equipment. A oneor two-step process for improving gum-containing gasoline is especially required.

The use of certain hydrocarbons as fumigant carriers or in special chemical processes is difficult at times, due to their liquid state and volatility characteristics. It is obvious that a crystalline material containing specific hydrocarbons, from which the latter could be readily separated at will, would be of great use for many purposes.

It is an object of this invention to provide new chemical complexes of hydrocarbons. It is another object of this invention to provide new crystalline materials from which hydrocarbons may be readily obtained. It is a further object of this invention to provide a method for forming such complexes. It is still another object of this invention to provide methods for the separation of hydrocarbons into desired fractions. One object in this respect is the separation of isoparaffins and naphthenes from aromatics andnormal paraflins. It is a related object of the present invention to improve the processing and quality of hydrocarbon mixtures, especially petroleum fractions. Other objects will become apparent from the following discussion.

Now, in accordance with this invention, it has been found that certain hydrocarbons form complexes with thiourea. Further, it has been found that crystalline complexes of thiourea and hydrocarbons may be obtained. More particularly, it has been found that the isoparaffins, naphthenes, isoolefins and cycloolefins readily form crystalline complexes with thiourea, and, further, that such crystalline complexes may be formed with the pure hydrocarbons or with the latter in admixture with other materials. Also in accordance with this invention it has been found that the formation of these compounds enables the separation, concentration and purification of specific hydrocarbons from impurities or diluting materials. Moreover,'it has been found that, due to the peculiarities of solubility and stability of the crystalline materials so obtained, remarkably pure individual hydrocarbons may be obtained. and petroleum fractions of outstanding characteristics may be formed.

The exact nature of the complexes is not known at the present time. However, as near as can be ascertained at present, the complexes appear to be molecular in character, both the hydrocarbon and the thiourea being readily recoverable therefrom in substantially pure form. The complexes, therefore, appear to be similar to compounds containing a solvent of crystallization, and possibly may be formed by hydrogen bonding. The ratio of mols of thiourea to mols of hydrocarbon varies with the molecular weight of the hydrocarbon and with the method of forming the complex. When the complexes are formed at about room temperature, as more fully described hereinafter, approximately three mols of thiourea form a complex with each four carbon atoms of the hydrocarbon. Thus, on a weight basis, there is an approximately constant ratio of about 3 to 4 parts thiourea for each part of hydrocarbon.

If other conditions of formation are employed the complexes may be quite different from those described above. For example, they may contain other ratios of thiourea to hydrocarbon, and/or they may contain a solvent of crystallization, such as alcohol or water. When the mixture of hydrocarbon is heated above about C. for a short time before allowing crystallization to occur, the crystal complexes contain lesser amounts structures.

of thiourea than those above, and usually have an approximate thiourea hydrocarbon weight ratio of 1:1. On a mol basis, complexes so formed usually will have a molar ratio of 2:1:1 thiourea hydrocarbon solvent. When using the solvent separation method more fully described hereinafter the ratio of thiourea to hydrocarbon may be even less than in the several types described above.

The complexes of hydrocarbons and thiourea are of two general types: those which are crystallin and those which are non-crystalline, usually fluid or oily in character. The crystalline type complexes are well defined in structure, having measurable angle and face characteristics.

The crystalline complexes of the individual hydrocarbons have sharp melting points, resolution into the two components thereof usually taking place after a short heating period, in the absence of other factors affecting the crystalline structure. While the crystal structure varies within wide limits, the complexes are generally needlelike in form, and can be made either in very small, short form or in the proper environment can be made to form coarse,-easily fllterable The latter are preferred for production on a large scale, since filtration problems thus are minimized.

When separations of fractions or types of hydrocarbons, rather than pure specific hydrocarbons, are desired (as in the preparation of improved petroleum fractions), use may be made of procedures whereby the non-crystalline complexes are obtained. These procedures, more fully described hereinafter, involve the use of moderately elevated temperatures, and/or the use of larger amounts of selective solvents than are required when preparing the crystalline complexes. While crystalline complexes usually may be derived from the non-crystalline type, this may not be necessary or even desirable for many purposes.

In general, the thiourea-hydrocarbon complexes are insoluble in water, or are soluble therein only to a slight extent. Further, this low water-solubility decreases with the ratio of thiourea to hydrocarbon in the complexes. The crystalline complexes are only sparingly soluble in organic materials such asalcohols, glycols and inert hydrocarbons. On the other hand, the noncrystalline complexes, while substantially insoluble in aqueous media, are somewhat soluble or dispel-sable in some media, particularly inert hydrocarbons.

As noted herebefore, crystalline complexes of thiourea, and hydrocarbons may be formed by treating either single hydrocarbons or mixtures thereof with thiourea. While the complex formation is simplified when only single hydrocarbons are so treated, generally the practical commercial applications of the principles involved as described herein, are separations of mixtures of hydrocarbons into desired components or fractions.

When complex formation is conducted at or below room temperature the two'types of hydrocarbons which form complexes with thiourea most readily are the isoparafi'ms and naphthenes. Other types of hydrocarbons which form complexes with thiourea are those having a predominating member which is an isoparafiin radical or a naphthene radical, such as alkaryl hydrocarbons wherein at least one alkyl group is an isoparaflin radical of about six or more carbon atoms.

Isoparaffins which form complexes with th ourea include isobutane, isopentane, 2,2-dimethylpropane, isohexane, 2,3-dimethylbutane, 2-methylpentanc, 3-methylpentane, 2-ethylbutane, 2- ethylpropane, 1,1-climethylpentane, 1,2-d methy1- pentane, l3-dimethylpentane, 1,4-dimethylpen- -tane, Z-et'nylpentane, 3-ethylpentane, 2-n-propylbutane, 2-isopropylbutane, 2-methy1hexane, 3- methylhexane, 2,2-dimethylpentane, 2,3-dimethylpentane, 2,4 dimethylpentane, 3,3-dimethylpentane, 2,2,3-trimet-hylbutane, Z-methylheptane, 3-methylheptane, 4-methylheptane, 3-ethylheX- ane, 2,2 d methylhexane, 2,3 dimethylhexane, ZA-dimethylhexane, 2,5-dimethylhexane, 3,3-dimethylhexane, 3,4-dimethylhexane, 2,2,3-trimethylpentane, 2,2,4-trimethylpentane, 2,3,3-t1'imethylpentane, 2,3,4 trimethylpentane, 2,23,3- tetramethylbutane, 2-methyl-3-ethylpentane, 3- methyl-B-ethylpentane, 2-mcthyloctane, S-methyloctane, -methyloctane, 2,2-dimethylheptane, 2,3-d methylheptane, 2,4-dimethylheptane, 2,5- dimethylhcptane, 2.6-dimethylheptane, 3,3-dimethylheptane, 3,4-dimethylheptane, 3-ethy1heptane, 4-ethy1heptane, 2,2,3-trimethylhexane, 2,2,4- trimethylhexane, 2,2,5-trimethylhexane, 2,3,3-trimethylhexane, 2,3,5-trimethylhexane, 2,4.4-trimethylhexane, 3,3,4-trimethylhexane, z-methyl- B-ethylhexane, 2-methyl--cthylhexane, 2,2,13,3- tetramethylpentane, 224,4 tctramethylpentane, 3,2-diethylpentane. 2,2-dimcthy1-3-ethylpentane, 2,3-dimethyl-3-ethylpentane, 2,4-dimethyl-3-ethylpc-ntane, 2,2,3,4-tetramethylpentane, 2-methylnonane, 3-methylnonane, i-methylnonane, 5- methylnonane, 2,2-dimethyloctane, 2,3-dimethyloctane, 2,4-dimethyloctane, 2,5-dimethyloctane, 2,6-dimethyloctane, 2,7-dimethyloctane, 3,3-diiii methyloctane, 3,4-dimethyloctane, 3,6-dimethyloctane, 4,5-dimethyloctane, 3-ethy1octane, 2,2,3- trimethylheptane, 2,2,6-trimethylheptane, 2,3,6- trimethylheptane, 2,4,4-trimethylheptane, 2,4,6- trimethylheptane, 3,3,5 trimethylheptane, 3 methyl-3-ethylheptane, 4-propylheptane, 4-isopropylheptane, 2,2,3,3-tetramethy1hexane,2,23,4- tetramethylhexane, 2,2,5,5 tetramethylhexane, 2,2-dimethyl-4-ethylhexane, 3,3,4,4-tetramethylhexane, 3,3 diethylhexane, 3,4 diethylhexane, 2,2,4-trimethylheptane, 2,2,4,5 tetramethylhex ane, 2-methyl-5-ethylheptane, 4-methyldecane, S-methyldecane, 2,3-dimethylnonane, 2,4-dimethylnonane, 2,5-dimethylnonane, 2,6-dimethylnonane, 3,3-dimethylnonane, 4-ethylnonane, 5-ethylonane, 2,3,7-trimethyloctane, 2,4,7-trimethyloctane, 2,2,3,3-tetramethylheptane, 2,2,4-trimethyloctane, 2,2,4,6-tetramethy1heptane, 2,2,4,5-tetramethylheptane, 3-methylundecane, 4-methylundecane, 2,3-dimethyldecane, 2,5-dimethyldecane, 2,6-dimethyldecane, 2,9-dimethyldccane, 3-ethyldecane 5-propylnonane, 2,2,7,7 -tetramethyloctane, 2,3,6}? tetramethyloctane, 2,4,5}? tetramethyloctane, 3,3,6,6-tetramethyloctane, 2-methyl-5 propyloctane, 3,6 diethyloctane, 2 ,6-dimethyl 3 isopropylheptane, 4,5 -diethyloctane, 2,2,4,6,6 pentamethylheptane, 2,2,4,4,6 pentamethylheptane, 5-methyldodecane, 2,10-dimethylundecane, 2,5,9-trimethyldecane, 4-propyldecane, 4-ethylundccane, S-butylnonane, 2,11-dimethyldodecane, 4,5 -diisopropyloctane, 2,7-dimethyl-4,5-diethy1octane, 4-propylundecane, 2,7- dimethyl 4 isobutyloctane, 2,6,10-trimethyldodecane, 2,6,1l-trimethyldodecane, 6 -methyl-'7- ethyldodecane, 5-propyldodecane, fi-propyldodecane, 4-methyl-6-propylundecane, 6,9-climethyltetradecane, 7,8 dimethyltetradecane, 3-ethyltetradecane, 5,7-diethyldodecane, 2,6,7,11-t-etramethyldodecane, 4,7-dipropyldecane, 2,2,3,3,6,- 6,7,7-octamethyloctane, 3,12 diethyltetraclecane, 2,6,11-trimethyl-9-isobutyld0decane, 2,6-dimethyloctadecane, 5,7,9-triethy1tetradecane, z-methyl- 4-isobutylhexadecane, 2,9 dimethyl-5,6-diisoamyldecane, 4 8,13,17 tetramethylicosane, 2,11-dimethyl-5,8 diisoamyldodecane, lo-nonyl-nonadecane, 2,6,10,l4,18,22 hexamethyltetracosane, 2,6,12,16-tetramethyl 9- (2,6dimethyloctyl) heptadecane, etc.

As stated hereinbefore another type of hydrocarbon which readily forms complexes with thiourea is that of the naphthenes. Typical species of this group include cyclopropane, methylcyclopropane, 1.l-dimethyl-cyclopropane 1 2-dimethylcyclopropane, ethylcyclopropane, 1,1,2-trimethylcyclopropane, 1,2,3-trimethylcyclopropane, 1- methyl-2-ethylcyclopropane, propylcyclopropane, l-methyl 2 propylcyclopropane, cyclobutane, methylcyclobutane, ethylcyclobutane, 1,2-dimethylcyclobvtane. propylcyclobutane, isopronylcyclo butane, 1.2-diisopropylcyclobutane, 1,2-dimethyl- 3,4-diethylcyclobutane, 1,1,2,2-tetramethyl-3,4- diisopropylcyclobutane, cyclopentane, methylcyclopentane, 1,1-dimethylcyclopentane, 1,2-dimethylcyclopentane, 1,B-dimethylcyclopentane, ethylcyclopentane, propylcyclopentane, isopropylcyclopentane, 1,1,3-trimethylcyclopentane. lmethyl-2-ethylcyclopentane, l-methyl-S-ethylcycopentane, butylcyclopentane, isobutylcyclopentane, 1 methyl 2 propylcyclopentane, 1- methyl-3-propylcyclopentane, 1,3 dimethyl-2- ethylcyclopentane, 1,3-dimethyl 5 ethylcyclopentane, 1,1-diethylcyclopentane, amylcyclopentane, isoamylcyclopentane, 2-cyclopentylpentane, 1-methyl-3-butylcyclopentane, 1-methyl-2,5-diethylcyclopentane, 1,2,3-trimethy1-4-isopropy1cy- 7. clopentane, heptylcyclopentane, cyclohexane, methylcyclohexane, ethylcyclohexane, 1,1-dimethylcyclohexane, 1,2-dimethylcyclohexane, 1,3- dimethylcyclohexane, 1,2,3 trimethylcyclohexane, 1,3,5-trimethylcyclohexane, butylcyclohexane, 1-methyl-4-ethylcyclohexane, 1-methyl-3- propylcyclohexane, 1-methyl-3-isopropylcyclo= hexane, 1,3-dimethyl--ethylcyclohexane, 1,3- diethylcyclohexane, amylcyclohexane, pentamethylcyclohexane, 1,2-dimethyl-3,6-diethylcyclohexane, -cyclohexylheptane, 3-cyclohexyl-3- ethylpentane, triisopropylcyclohexane, 2,8-dimethyl-5-ethyl-5-cyclohexylnonane, l-methyl-iisopropyl-2-dodecylcyclohexane, octadecyclohexane, propylcycloheptane, and polycyclic naphthenes such as decalin.

Iso-olefins which form complexes with thiourea include monoiso-olefins such as'2,3-dimethyl-l-butene, 3-methyl-2-ethyl-l-butene, 2,6-dimethyl-l-heptene, 2,3,4,4-tetramethyl 1 pentene, etc., and diiso-olefins such as 2,3-dimethyl- 1,3-butadiene, etc.

Cyclo-olefins which may be separated by the present process include 2,3-dimethyl-1-cyclopentene, 1-ethyl-2-methyl-1-cyclohexene and cyclodiolefins such as 3,3-dimethy1-1,4-cyclohexadiene and terpenes such as alpha-pinene.

The hydrocarbon or mixtures thereof with which a thiourea complex is to be formed may be contacted with thiourea either in the presence of a hydrocarbon solvent or diluent or in the absence thereof. Solvents are particularly practical when the hydrocarbon is solid at the temperature at which complex formation is to occur, although such formation may be conducted by treating the melted hydrocarbon (such as paraffin wax) if the melting point is relatively low. Hydrocarbon diluents or solvents are regarded, for the purpose of this discussion, as any material which does not readily form a crystalline complex with thiourea at the temperature and under the other conditions of contacting, even though they may form such complexes therewith under other sets of conditions. Preferably especially when the contacting temperature is about 50 C. or lower, the preferred diluents or solvents are other hydrocarbons, that is, hydrocarbons which are relatively inert toward thiourea under the contacting conditions. Suitable hydrocarbons for this purpose are normal hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane, dodecane and mixtures thereof, as well as aromatics such as benzene, toluene, xylenes, etc.

The solvent or diluent may be present as an impurity, such as in cracked gasoline. In the latter case, the gasoline is treated with thiourea in order to isolate isooctane and other hydrocarbons having a high octane rating, while the normal paraflins and aromatics usually present therewith constitute a diluent for the reaction.

The presence of a diluent or solvent for the hydrocarbons is desirable in that, upon treatment of such a hydrocarbon mixture a fllterable slurry of the complex in the diluent is formed, rather than a substantially solid mass of the complex. Subsequently, the complex may be separated from the slurry, as more particularly described thereinafter, and is readily available for purification and/or for regeneration of the components of the complex, also more fully described later.

In the absence of a suflicient amount of a suitable diluent, i. e., when asubstantially solid complex mass is formed, it is necessary to use other means such as crushing, transportation by conveyor, etc., for recovering and transporting the complex. Therefore. it is desirable to have a diluent active hydrocarbon ratio of at least about 1:1. From a practical standpoint, it usually is diflicult to satisfactorily separate a complex from a mixture containing a ratio of diluent to active hydrocarbon greater than about 25:1, although such separations are possible under special conditions, especially when the temperature during thiourea contacting and/or during crystallization is sufliciently low.

For the purpose of contacting thiourea with hydrocarbons, either in the presence or absence of a hydrocarbon, a thiourea solvent also may or may not be used. Preferably enough of a thiourea solvent is present so that at least a minor amount of the thiourea is in solution at all times. Alternatively, the thiourea may be contacted with hydrocarbons while it is completely in solution. When this latter condition is used it is a preferred practice to employ a substantially saturated solution of thiourea, although more dilute solutions thereof may be utilized under conditions to be described more fully hereinafter.

The type of thiourea solvent present during complex formation has a powerful effect upon the results obtained. It has been discovered, in accordance with one phase of the present invention, that by choosing special thiourea solvents or mixtures thereof a predetermined fraction or group of hydrocarbons will form thiourea complexes. For example, by using an aqueous alcoholic thiourea solvent for the thiourea, and varying the ratio of water to alcohol, an extremely close control is obtained over the type of hydrocarbon which will form complexes with the thiourea. This phenomenon may be utilized, for example, in the treatment of isomerization mixtures, where substantially complete removal of isoparaffins is essential before recycling unreacted material back through the catalyst tower. In other cases, for example, when it is desired to extract only a portion of isoparaflins or naphthenes in order to produce a finished blend rather than a blending stock, the thiourea solvent may be adjusted or chosen so that only partial removal of the active hydrocarbons is effected.

It is preferred practice to choose a thiourea sol-' vent which is substantially immiscible with the medium from which thiourea-hydrocarbon complexes are to be obtained. Partiiularly useful solvents for this purpose are water, the lower monohydric alcohols and the lower polyhydric alcohols such as the glycols. Mixtures of these solvents are useful for the close control of complex formation discussed above, and aqueous alcoholic (especially water methyl alcohol) mixtures are preferred, since they are easily recoverable, low in viscosity, contain no detrimental color or other impurities, and are good solvents for thiourea but are substantially immiscible with hydrocarbons and hydrocarbon mixtures of nearly all types.

The ratio of thiourea to hydrocarbons capable of forming separable complexes therewith may vary within wide limits, dependent upon the type of complex desired, the rate of complex formation necessary for efficient operation, the temperature of the reaction, the dilution of the active hydrocarbons, the dilution of thethiourea, and other factors affecting the operation. It is preferred practice, when a maximum removal of active hydrocarbons is desired, to contact the .thiourea.

latter with a substantial excess of thiourea, that is, an amount in excess of that with which the hydrocarbon will combine under the other conditions of contacting.

As pointed out hereinbefore, complexes may be formed having varying amounts of thiourea combined in molecular complex with the hydrocarbons. When the temperature or other conditions during complex formation are such that about three mols of thiourea combined with about every four carbon atoms of the hydrocarbon, it is preferred'practice to contact the hydrocarbon with an amount of thiourea somewhat in excess of this ratio. Again, if more elevated temperatures are employed, so that crystalline complexes are formed having thioureazhydrocarbon ratios from about 1:1 to about 2:1, amounts of thiourea in excess of these respective ratios should be used if complete complex formation is desired in the minimum length of time. Also, if such complexes contain solvent of crystallization, such as alcohol or water, care should be exercised that a sufficient quantity of the solvent is present for this purpose, preferably in addition to that amount required tomaintain the desired solution concentration of the thiourea.

When the hydrocarbons are present in very dilute form, for example, in an isomerization 'mixture from which a major portion of the isoparaffins have been removed, it is a preferred practice to contact the mixture with a large excess of thiourea, since by this method maximum complex formation takes place. I

While the thiourea treatment of active hydrocarbons may take place in a single stage, at times it is preferable to cause complex formation in a series of stages, using either a constant concentration of thiourea solution in each stage to form successive batches of the same complex, or varying the thiourea solution concentration to obtain different complexes in each stage. A fuller description of these processes is. given hereinafter.

The temperature at which thiourea is contacted with hydrocarbons is an important factor in determining the extent of complex crystallization or separation of specific hydrocarbons, as well as in determining what hydrocarbons will form separable complexes with thiourea. Moreover, the temperature at which complex formation takes place determines the ratio of thiourea:hydrocarbon necessary to form a complex.

' This last factor may be utilized, for example,

where an active hydrocarbon is present inrelatively small quantities as compared with an hydrocarbon which is substantially inert toward below a crystalline complex may be formed which At temperatures of about 50C. or

has a relatively high proportion of thiourea.

Thus, even though only traces of the isoparaflin, naphthene or other active hydrocarbon may be present, the complex formed under the above conditions usually will be of sufficient bulk to be readily separable from the mixture.

If, however, it is necessary to remove relatively large hydrocarbon-fractions from a mixture by treatment with thiourea, it is ordinarily desirable to elevate the temperature above about 50 C. since the complex which is formed under these conditions will have a minimum proportion of thiourea, thus minimizing processing and recovery problems. I

In accordance with one phase of the present invention, it has been found that a critical temperature exists (all other conditions being equal) above which a given complex will not crystallize.

Thus, if the mixture of hydrocarbons which form complexes with thiourea at a given temperature includes undesirable specific members or fractions, it is possible to depress or even eliminate said fractions from crystallizing with thiourea simply by changing the temperature of contact so that the undesirable fractions remain in solution while the desirable fraction crystallizes out as a complex with thiourea.

This phenomenon may be utilized in' a variety of processes wherein the mixture of hydrocarbons is passed through a series of temperature gradients. For instance, after the step described in the paragraph above has been carried out, it is possible to lower the temperature, contact the hydrocarbon mixture with thiourea, and take out a second fraction. This system of fractional crystallization is subject to extremely close control, and thus permits remarkably accurate fractiona tion of a mixture into its individual components or types of components.

Some hydrocarbons crystallize more readily with thiourea when a complex is formed which has a minimum thiourea content and/ or solvent of crystallization. For these cases it is advisable to warm the hydrocarbons with thiourea until such a complex is formed.

For any given complex, once it has been formed, the lower the crystallizing temperature the greater the yield of the complex. Hence, after formation of a complex it may be advisable to cool the mixture considerably in order to obtain maximum recovery of a specific hydrocarbon-thiourea crystalline material. In accordance with procedures outlined in preceding paragraphs, it is necessary to conduct the cooling step so that a minimum amount of undesired fractions or hydrocarbon complexes crystallize out at the same time. It is necessary at times to resort to the stepwise temperature change, as outlined above, in order to separate fractions as desired. Combinations of changes in thiourea solvent, thiourea concentration, temperature of complex formation and temperature of crystallization may be used in batchwise, continuous or recycling process in order to obtain any desired hydrocarbon or mixture of hydrocarbon.

Another important controlling feature of the process of the present invention is the manner in which the hydrocarbon or hydrocarbon mixture is contacted with thiourea. Basically, the contacting step variations may be related in nomenclature to catalytic treatments of petroleum prod- 1. Concurrent fluid processes, whereby a solution of thiourea is introduced into the hydrocarbon feed line.

2. Countercurrent fluid processes, whereby a solution of thiourea is passed down through a rising column of hydrocarbons.

.3. Fluid fixed bed processes, whereby the hydrocarbon is passed through a stationary column of thiourea solution.

. Moving bed processes, whereby solid thiourea proceedes to move countercurrently to the hydrocarbon feed.

5. Slurry processes, whereby a mixture of solid thiourea and thiourea solution moves concurrently or countercurrently with the hydrocarbon feed.

6. Emulsion processes, whereby solutions of thiourea are emulsified, at least momentarily with the hydrocarbon feed.

' area is a pipe system, which not only allows time for complete crystallization, but also permits accurate and rapid temperature control of the area. This later point is an important factor in deter- -mining the relative success of the process of the present invention. If the hydrocarbon feed contains a high proportion of hydrocarbons which will crystallize with thiourea, it is possible to allow only partial crystallization at any given time, with several stages of filtration. The time and degree of crystallization may be controlled, as described hereinbefore, by adding thiourea solution at more than one point in the system, by temperature control, by control of the concentration of thiourea, or by other means.

The second means of contacting, namely, countercurrent fluid processes, is especially suitable for the complete utilization of thiourea solutions and for extractive crystallization of relatively minor amounts of active hydrocarbons in the presence of a correspondingly large amount of inert hydrocarbons or other diluent. In carrying out countercurrent fluid extractive crystallization suitable equipment includes a make-up tank for thiourea solution, a contacting tower with hydrocarbon feed entering at the bottom and thiourea solution being introduced from the top, an optional crystallizing area (crystallization may take place in the contacting tower), a separation area such as a settling tank or centrifuge, recovery means for the railinate, spent thiourea solution and means for separating the hydrocarbon from its crystalline complex. If the contacting tower is-used as the crystallizing area it is preferred practice to have at least one part of the tower cooled so as to allow maximum crystallization, when such. is desired. Countercurrent fluid ex traction processes are especially adaptable for recycling steps, either for the thiourea so ution or partially extracted hydrocarbon or hydrocarbon mixture. It may be used, for example, in conjunction with an alkylation process, fractions be ing removed by crystallization with thiourea in order to separate the various types of alkylates present in the mixture coming from the alkylation system.

The fluid fixed bed processes are especially use ful where a simple flow plan is desirable, since the essential feature of such a process is a stationary column of thiourea solution. In carrying out such a process it is desirable to at least partially fill a column or tower with thiourea solution and subsequently pass the hydrocarbon feed therethrough, preferably with an inlet near the bottom of the column. It is also preferred practice to maintain the temperature, the rate of passage and other conditions within the tower in such a state that little or no crystallization takes place therein, but subsequently allowing the hyl2 drocarboncomplex and remaining feed to pass to crystallizing and separating areas. The latter is preferably separated from the contacting tower to allow simplification of equipment design,'but

5 the contacting tower may be constructed so as to be suitable for settling and crystal removal if such is desired. In any case there is usually a certain amount of build-up of crystalline complex due to local cooling etc., so that allowance should be made for a clean-out or draw-off valve at or near the bottom of the tank. As hydrocarbon feed passes through the stationary thiourea solution the latter gradually becomes depleted or diluted unless it is replenished from time to time. A preferred alternative to cope with the situation is the substantially continuous introduction of solid thiourea and/or concentrated thiourea solution into the main body of the column, such as by a feeder line controlled automatically or manually, as desired.

Another system of contacting thiourea with hydrocarbons is the solid fixed bed process. whereby the hydrocarbon feed is passed through a fixed bed of solid thiourea. Such a process may operate under special conditions in the absence of a. thiourea solvent, but it is preferred practice to introduce a controlled amount of water into the system at the time of or prior to contacting thiourea with the hydrocarbon. In effect, this produces a saturated solution of thiourea in situ. If the latter step is incorporated in the process, it is still more preferred that the thiourea solvent be introduced into the hydrocarbon prior to contacting with thiourea, and that it be finely and uniformly distributed therethrough, if necessary by use of an emulsifying agent, but preferably in the latters absence.

When the solid fixed bed system is employed it is preferable for continuous operation to maintain the temperature and other contact conditions such as rate of flow so that crystallization does not occur in the bed. Thus it is better to provide a crystallizing area wherein the hydrocarbons and fluid complex are received from the contacting zone, and in which crystallization may occur, followed by separation of thecrystals from any diluent present. As in the case of the fluid fixed bed process described above, the solid fixed bed will diminish in size and effectiveness unless additional solid thiourea is introduced. A convenient method of doing this is to introduce the solid thiourea into the hydrocarbon feed as it enters the contacting zone, but under conditions such that crystallization with the hydrocarbon does not occur.

The moving bed type of process may be utilized, wherein solid thiourea moves concurrently or countercurrently with the hydrocarbon feed. This method is easily applied and has the advantage that a constant and controlled amount of thiourea is always present. Preferably water or alcohol is present as an internal dispersion in the hydrocarbon, having been distributed therethrough prior to contacting with thiourea. Alternatively, complex formation may be conducted in the absence of a thiourea solvent, or contact of the thiourea and hydrocarbon may be followed by introduction of water. It is preferable to remove most of the excess solid thiourea prior to allowing crystallization to occur. The moving bed process is adapted for combination with the fixed bed process, whereby solid thiourea is introduced into the hydrocarbon stream and eventually reaches the fixed bed of thiourea. Under some circumstances it is desirable to add an inert col- 13 loid or other dispersing agent to keep water and/or thiourea uniformly and finely distributed throughout the hydrocarbon. Preferably the colloid is coagulable or otherwise removable at a late stage in the process, so that the hydrocarbon products are not contaminated therewith.

Since it is usually advantageous to maintain a saturated solution of thiourea in contact with the hydrocarbons, a slurry process may be employed, combining the fluid processes and the moving bed process. This may be accomplished by havin an entirely concurrent system, or by combined systems, such as passing solid thiourea countercurrently to a mixture of the hydrocarbons and thiourea solution, or by passing thiourea solution countercurrently to a mixture of solid thiourea and hydrocarbons.

As pointed out hereinbefore it is advantageous at times to maintain an emulsion of thiourea solution in the hydrocarbons, at least momentarily. Some hydrocarbons form complexes with thiourea rather slowly. In such cases an emulsion of solutions of the latter with the hydrocarbon may be made and stored or passed through an extended pipe system or reactor until crystals form. Such emulsions may be either water-in-oil or oil-inwater types, but the former is preferred, since the volume of water usually is smaller than the volume of hydrocarbons present.

Solvent extraction processes involve the use of a lean solvent for the complexes from which various fractions may be extracted by the use of better solvents therefor. It will be understood that these types of contacting processes are only representative of the various means whereby thiourea may be reacted with hydrocarbons, and furthermore that combinations and modifications of the above processes may be made in order to obtain a particular product.

Subsequent to contactin thiourea with hydrocarbons, as described above, the complexes so formed must be separated from the main body of hydrocarbons, diluents, excess thiourea solution, impurities, etc. This may be accomplished in various ways, such as by decantation, settling, filtration or centrifuging. Decantation and settling are especially useful when the crystalline complexes are relatively heavy and separate sharply and readily from the other components of the system. When settling is employed it is preferable to allow it to take placein a settling tank with continuous or semi-continuous withdrawal of efiluent from the top and complex at the bottom. Alternatively, the complex may be separated as a suspension in an aqueous phase and thereafter subjected to regeneration, either with or without a filtration step.

If the hydrocarbon mixture comprises a heavy oil, such as a lubricating oil or Diesel oil, settling and decantation are usually insuflicient by themselves to produce satisfactory separation. In such cases centrifuging or filtration usually are necessary, either alone or supplementary to decantation and/or settling. An eflicient method comprises allowing settling for the removal of the bulk of the crystalline complex, followed by filtration of the'efiiuent, which contains residual crystals held in suspension due to their finely divided form or the viscosity of the liquid components of the mixture.

After separation the complex may be purified by washing with a relatively inert material such as a normal or aromatic hydrocarbon (pentane, hexane, heptane, benzene, toluene, etc.). It is a preferred practice during any purification step to keep temperatures as low as is practical, consistent with the prevention of losses of the complex by solution in the wash liquors.

\ The formation, separation and purification of the hydrocarbon-thiourea complexes having been accomplished as described above, there remains the step of decomposing the complex in order to recover the hydrocarbon. While a number of methods have been found for effecting such decomposition. the following methods or combinations thereof have been found to be the most satisfactory for general use:

(a) Dry heat (b) Dry distillation (c) Distillation with hot dry gases (d) Steam distillation (e) Application of a thiourea solvent (1) Application of a hydrocarbon solvent The complexes, as has been pointed out hereinbefore, are relatively unstable formations, apparently loose combinations involving hydrogen bonding or some form of molecular attraction, the exact nature of which has not been deduced. It has been found that due to their unstable character, splitting into the hydrocarbon and thiourea components thereof may be readily accomplished. The application of mild heat to the crystalline complexes results in liquifying followed by stratification. Thus, by heating to a temperature of the order of about F. such stratification occurs. It is a simple matter to separate the hydrocarbon layer from the'thiourea. This method is particularlyadapted to the decomposition of complexes which contain a solvent of crystallization, such as water or alcohol. In such a case, upon heating, the heated crystals form two layers, one of which contains the hydrocarbons the other being a solution of thiourea. The latter then may be separated from the hydrocarbons and recycled for the preparation of additional complexes.

A second method of decomposition comprises dry distillation, wherein the above method of dry heating is combined with a distillation step. This modification is especially useful where relatively volatile hydrocarbons are involved. Moreover this method may be used as a means of still further fractionating the hydrocarbons. As they are recovered by dry heating, a mixture of hydrocarbons is obtained, assuming that more than one hydrocarbon is present. But by adding a distillation step to the dry heating, the hydrocarbons are easily recovered as a series of fractions. At times itis desirable to distill the entire hydrocarbon layer, leaving nothing but thiourea or a solution thereof in the still. Again, only a portion of the desired product need be recovered by distillation, the remainder being obtained by, separation from the thiourea. It is preferable, Wherever heat is applied, to use the lowest temperatures consistent with maximum efficient recovery. It will be recognized that distillation under diminished pressure is advisable at times, in any of the distillation processes being discussed. Since thiourea is somewhat unstable when heated it is preferred practice to remove it from the heating zone as quickly as possible after its regeneration, and to cause such regeneration to occur at relatively mild temperatures.

Another method of regenerating hydrocarbons from their complexes involves dry heating while hot dry gases are passed through the mixture at such temperatures and under such pressures as will permit the hot gases to remove at least a portion of the hydrocarbons, This method is especially valuabl where hydrocarbons are present which are somewhat subject to thermal decan be separated as described above. Furthermore, due to the presence of the modifying composition. Preferably the gases used for this substantially inert at the distillation and highly volatile at room temperawhile carbon dioxide purpose are temperature ture. Nitrogen is preferred, also may be used.

The use of steam distillation is a preferred method for hydrocarbon regeneration. By this means substantially lower temperatures are necessary for hydrocarbon recovery, and decomposition of thiourea and other components of the mixture is held to a minimum. Steam distillation is particularly applicable to the recovery of hydrocarbons having high boiling points or which would carbonize to a certain extent if distilled by dry heat alone. The use of steam distillation, particularly using dry steam, also facilitates the recovery and/or purification of the regenerated thiourea, since a portion of the steam condenses and acts as a solvent for thiourea. The solution of thiourea thus formed is immediately available for recycling in a continuous or semi-continuous process.

Another method of hydrocarbon regeneration comprises the addition of a thiourea solvent to the crystalline complex. Suitable solvents for this purpose are water, alcohols or glycols, and water is preferred, although aqueous alcohol also is satisfactory. It usually is necessary to apply some heat in order to decompose the complex. Upon mild heating, the stratification described above is evident, a solution of the regenerated thiourea separating from the layer of the regenerated hydrocarbons. If it is necessary to fractionate the hydrocarbons, it is preferred practice to remove them from the thiourea solution and then subject the mixture to fractional distillation.

A further preferred means of regenerating hydrocarbons from their thiourea complexes involves the addition of a hydrocarbon solvent, such as ether, to the complex, preferably followed by mild heating under pressure. This method is particularly useful when the hydrocarbon to be regenerated is a highly viscous liquid or a wax-like solid 'at room temperature. When the mixture of complex and ether are warmed, the thiourea which separates can be filtered or otherwise disposed of leaving a solution of the hydrocarbon.

The last two methods can be combined for example when the regenerated thiourea is to be recycled and the regenerated hydrocarbon is difficult to handle except as a solution.

It has been pointed out hereinbefore that the major purpose of treating hydrocarbons with thiourea is the separation of hydrocarbon mixtures into preferred types or members. Thus, if a hydrocarbon mixture, such as petroleum, contains aromatics, normal paraflins, cycloparafllns and isoparafiins, it is a simple matter to separate the aromatics and normal paraffins from the other two types by treatment with thiourea. Thereby the cycloparafllns and isoparallins are readily crystallized with thiourea, while the other types remain unchanged under the conditions described hereinbefore. Further separation of types is possible by modifications of or additions to the thiourea process.

One modification of the present process comprises the addition of compounds such as ethanolamines or acetamide to an alcoholic solution of thiourea, following which the mixture of hydrocarbons is treated therewith. Upon such treatment the isoparaflins and cycloparafiins form crystallin complexes with thiourea and agent in the alcohol, the normal parafiins separate therefrom as an immiscible layer, while the aromatics dissolve in the alcohol. Thereafter the two liquid layers may be separated and the aromatics and normal parafllns separately recovered.

This latter process may be varied by treatment of the hydrocarbon mixture with alcoholic ethanolamines or acetamides prior to treatment with thiourea. By this procedure the aromatics may be removed from the system prior to thiourea complex formation. Alternatively the rafllnate, i. e. the fraction of a hydrocarbon oil not forming a complex with thiourea, may be treated with alcoholic acetamide or ethanolamine subsequent to thiourea complex separation, so that aromatic may be separated from the normal parafiins.

A versatile and useful modification of the process of the present invention is the'combination therewith of treatment of the hydrocarbon mixture with urea. The latter forms complexes with hydrocarbons of normal structure, both normal parafiins and normal olefins, but fails to form complexes with aromatics or isoparafiins.

.Since. these properties are in complete contranormal hydrocarbons thus formed, and treating the remainder of the hydrocarbon mixture with thiourea, as described hereinbefore, thus forming crystalline complexes of th isoparafilns and cycloparaflins. The latter can be regenerated as described above.

A further method for the separation of hydrocarbon mixtures into its component parts comprises initially treating the mixture with thioureaso as to separate the isoparaflins and cycloparaffins from the normal hydrocarbons and aromatics. If the rafiinate contains a preponderance of aromatics from which the normal paraflins must be separated, it should be treated with an aqueous or alcoholic solution of urea, separating the crystalline complexes, thus leaving substantially pure aromatic hydrocarbons. If the rafiinate comprises normal hydrocarbons contaminated with minor proportions of aromatics, it should be treated with an aromatic hydrocarbon solvent such as aniline, etc., or with an alcoholic solution of acetamide, so as to solvent extract the aromatics, leaving pure normal hydrocarbons.

The problem of purifying hydrocarbon mixtures comprising aromatics, such as benzene, toluene, etc., contaminated with minor amounts of normal hydrocarbons, isoparaffins and cycloparaflins is readily solved by treating with a combined solution of both urea and thiourea, separating the mixture of crystalline complexes thus formed, and thereby obtaining purified aromatic hydrocarbons.

These treatments and combinations of treatments are especially useful for the fractionation 17 of petroleum hydrocarbon mixtures, as described elsewhere in this specification.

A modified process comprises heating a hydrocarbon mixture with an aqueous solution of thiourea at a temperature above about 75 C. At these elevated temperatures the reaction mixture eventually separates into two layers, one containing the ,hydrocarbons and a major proportion of the complex, while the other is an aqueous layer containing a major portion of thiourea and a minor amount of a hydrocarbon complex. However, when the warm layers have been separated and cooled, the complex recovered from the first layer has a minimum thiourea hydrocarbon ratio, that is, about 2:1 on a molar basis, while the small amount of complex recovered from the aqueous layer has a molar ratio of about 6:1. Thus, where large amounts of a complex are to b formed, it is advantageous to utilize this modified method, since minimum quantities of thiourea are required.

Another means of producing complexes having low thiourea hydrocarbon ratios is by heating the hydrocarbons with thiourea in the presence of only a minor amount of water or alcohol at temperatures from about 50 C. to about 75 C. Within this range complexes are formed which have low ,thiourea hydrocarbon ratios, and which usually contain some solvent of crystallization. Layer separation usually does not occur, the complex being recovered upon cooling to produce crystallization.

Multi-stage Processes may be used for meeting special conditions and for effecting separation of closely allied types of hydrocarbons. For example, it is advantageous to have a resonably large fluid phase relative to the amounts of crystalline complex, since such a condition will facilitate handling, especially during a filtration step. If the hydrocarbons to be treated with thiourea contain a large proportion of those which will form crystalline complexes, a single complete crystallization may result in a practically solid mass, with any inert hydrocarbons and unreacted thiourea occluded on the crystals. In order to avoid obtaining such a contaminated mass, it is advisable to modify the process so that only partial crystallization takes place at any one time. This can be done in various ways, such as by making multi-stage addition of the thiourea required for complex formation with all the reactive hydrocarbons, and filtering off the crystals formed after each addition. Such additions may be uniform, but as the hydrocarbon mixture becomes leaner in fractions which will form crystalline complexes it is preferred that each thiourea addition be increased, since a relatively larger proportion of inert hydrocarbons will be present to aid in filtration.

Another means of producing gradual or stepwise crystallization is by temperature control. It has been ascertained that each hydrocarbon has a temperature above which crystallization will not occur, or will take place only at a reduced rate. Further, it has been found that with any given complex, the lower the crystallizing temperature the greater is the amount of complex which crystallizes out. Moreover, it has been found that each complex has a critical temperature above which itwill not crystallize out of a given reaction mixture. Each of these established facts may be utilized in determining the exact conditions to be used in treating a specific hydrocarbon or mixture thereof.

Thus, if it is desired to separate a more reactive hydrocarbon from one having less reactivity with thiourea, the mixture of hydrocarbons may be treated with thiourea below the critical reaction temperature of the second type. After removing the resulting complex, the hydrocarbon mixture may be heated with thiourea to a temperature at which the second type will react, thus forming a complex uncontaminated with that of the more reactive hydrocarbon.

Again, if a large enough proportion of a hydrocar'oon has been treated with thiourea, so that if crystallized in a single stage a thick mass of crystais would be formed, the temperature may be adiusted so that only a portion of the product crystallizes. Following filtration of these crystals, it is a simple matter to cool the filtrate until another batch of crystals have formed. This may continue in cycles until it becomes uneconomical to process the hydrocarbon filtrate further, after which the remaining filtrate may be discarded or recycled to feed with or without further treatment. I

The critical temperature of crystallization of each hydrocarbon complex may be utilized to separate or fractionate a mixed product. Thus, after formation of a mixture of complexes the temperature may be adjusted so that only one type crystallizes. After filtration of these, the filtrate may be cooled in order to cause crystallization of further types of complexes.

Another means of controlling crystallization is by varying the concentration of thiourea in its solvent, as outlined earlier in this sepcification. In a multi-stage process advantage may be taken of this by contacting a hydrocarbon mixture with a thiourea solution and removing the complex so formed. Subsequently, the filtrate may be treated with thiourea solution of a greater or less concentration in order to form complexes of different hydrocarbons.

Choice of solvent for either thiourea or hydrocarbons has been found to affect the type of complex formed and the extent to which a given complex will crystallize. In a multi-stage process, after removing one type of crystalline complex, a solvent, such as ether may be added to the filtrate. Since some of the hydrocarbon complexes are less soluble in ether-containing mixtures, fractional crystallization will occur, enabling the recovery of another fraction of crystals.

Some hydrocarbons, such as triptane, may be separated substantially completely from mixtures containing them. Others may be extracted from their mixtures to the extent of 50- 9570. In the latter case, the filtrate may be mew-camera ther treatment, either with'thiourea or with other reagents. Following extraction of certain hydrocarbons from their mixtures, the latter may be subjected to distillation, treatment with urea, treatment with a solvent for aromatics, etc;, in order to concentrate the active hydrocarbons be fore further treatment with thiourea.

The practical applications of the process of the present invention are numerous. For example, thiourea may be utilized to improve isomerization processes. In isomerization, a hydrocarbon feed is heated and isomerized in the presence of a catalyst such as hydrogen chloride. The mixture so obtained comprises normal hydrocarbons and their branched isomers. Under a given set of conditions there is always a maximum extent to which isomerization will occur. After stripping hydrogen chloride from the product, the mixture is subjected to fractional distillation. The normal hydrocarbons are then returned to l9 feed for another isomerization treatment. However, the fractional distillation always allows a minor amount of the isomerised product to remain in the normal feed. The inclusion isomerized hydrocarbon in the recycled feed to the reactor will reduce the net conversion to the isomerized product. Therefore, in order to free feed or recycled feed from branched isomers, the thiourea process may be used, thus producing a feed substantially free of all but normal hydrocarbons. The thiourea treatment may be applied before the feed reaches the isomerization reactor and/or after separation of isomerized product from unreacted feed stock by fractional distillation. Since the proportion of isomers as compared to normal hydrocarbons is small in these cases, it is preferred that low temperature complex formation, favoring the production of complexes having a relatively high thiourea hydrocarbon ratio. be used.

The'thiourea process applies in a like manner to improving stocks and recycled feed in alkylation processes. In such processes a mixture of alkylate and unreacted feed is produced .by passing a feed stockof oleflns and paramns through reactors containing catalysts such as concentrated cold sulfuric acid or hydrogen fluoride. Subsequent to alkylation, the mixed product is fractionated to remove most of the alkylate, while the remainder, comprising feed constituents and a small amount of alkylate is recycled through the alkylator. Unless this remaining alkylate is removed the efliciency of the allrylation process is reduced. Hence, by applying the thiourea process to the stock after removal of a substantial portion of the alkylate, the remainder of the latter may be removed as a thiourea complex. This may be done in one of two ways: either by forming complexes of both isoparaflln feed stock and the alkylate and subsequently separating the isoparaflins for introduction back into the recycling line; or by adjusting reaction conditions so that the simple isoparaflins are left unchanged, while the alkylate forms a complex and can be separated from the remaining fractions by crystallization.

In the production of aviation or motor gasoline, the thiourea process may be used to isolate the isoparafilns and naphthenes from straight run or processed gasoline. The concentrate so obtained may be used as such or for blending purposes. The rafllnate, after removal of arcmatics, for example by solvent extraction, may be used as feed for isomerization, dehydrocyclization or other processes for converting normal paraffins to improved products. The naphthene and isoparaflin fractions, isolated as thiourea complexes, may be used as feed stocks for hydro-' forming.

An important use of the thiourea process is the separation of specific naphthenes from mixtures thereof for the production of hig y Purified stocks to be used in polymerization processes, plastic manufacture, etc.

Triptane is outstanding in its ability to form crystalline complexes with thiourea. Hence, advantage may be taken of this in analysis for and recovery of trlptane from alkylates or other hydrocarbon mixtures.

Modifications of the complex are possible to produce special fractions, such as formation of the hydrochloride salts, acetate salts, etc. A preferred method for such formations is to Drepare the complexes as described hereinbefore and subsequently treat the complex, preferably in solution, with dilute hydrochloric acid or acetic anhydrlde, in the presence of any necessary catalysts. For example, the presence of sodium acetate during the formation of the complex-acetate facilitates acetylation.

While one of the primary uses of the crystalline complexes is for isolation of specific hydrocarbons or hydrocarbon fractions, the hydrocarbonthiourea complexes per se are useful for a number of purposes. They may be used for the fixation and storage of the more volatile hydrocarbons. They are useful in insecticides and fumigants. They are suitable for use in the preparation of pharmaceuticals and other chemical compounds.

The following examples illustrate the preparation of the thiourea-hydrocarbon complex and the use of the thiourea process in the fractionation of hydrocarbon mixtures.

EXAIMPLE I Table I Isoparailln hydrocarbons:

Isopentane Isooctane 2,3-dimethybutane 2,2,3-trimethylbutane Naphthenes Methyl cyclopentane Cyclohexane Methylcyclohexane Ethylcyclohexane 1,2-dimethylcyclohexane 1,3-dimethylcyclohexane 1,4-dimethylcyclohexane Decalin EXAIMPLEII The procedure described in Example I was repeated, using the normal paraflln and aromatic hydrocarbons listed in Table II. No crystalline complexes were formed in any case, at the temperature employed (22 C.)

Table II Normal parafllns:

Normal pentane Normal heptane Normal octane n-Hexadecane Aromatic hydrocarbons:

Benzene Toluene Xylenes EXAMPLEIII Various mixtures of hydrocarbons were treated with thioufea as described in Example I. Crystalline complexes were formed in each case. Table HI describes the original mixture and the thiourea complex obtained from each.

Table III sample Mixture Thlourea Complex A 50% normal hcptanc, 50% isooctane isooctane. B 959,, normal lluptanc, triptane triptane, O 90% normal hcpiam, triptane; .l Do. D 80% normal hcptanc triptane Do, 15.. 75% normal hcpumo, ','{.2,3-d|metl1ylbuta 2, 3-dlmethylbutane. F 50",, normal licplanc, 505; cyclohexanc cyclohexane.

G", 956,. normal hcplum', 5'2, cyclohexane Do, H 50% normal licplanc, 50% incthylcyclohexane mcthylcyclohexane. I 50% ll, 2-(limclhylcyclollcxane, 50% 1, 4-dimethylcy- Predominantly l, 4-dimcthylcyclohexana cln lcxane. J 50%1,4-dimcthylcyclohexane,50%ethylcyclohexane. Predominantly ethylcyclohexane.

EXAMPLE 1v Ten parts of 2,3-dimethylbutane and 60 parts of a 50% solution of thiourea in alcohol were intimately mixed at 10 C. A crystalline complex of thiourea and 2,3-dimethylbutane formed almost immediately. The crystals were filtered 01f, washed with normal pentane and subjected to steam distillation. The distillate contained 2,3-dimethylbutane while an aqueous solution of urea was formed in the still used for the distillation.

EXAMPLE V Ten parts of lA-dimethylcyclohexane and 60 parts of a 50% solution of thiourea in alcohol were intimately mixed at 17 C. The crystalline complex of thiourea and 1,4-dimethylcyclohexane, which formed immediately, was filtered and washed with normal pentane. When subjected to steam distillation, the complex decomposed, 1,4-dimethylcyclohexane passing over in the distillate, while the thiourea remained in the still in aqueous solution.

EXAMPLE VI Twenty-five parts of isooctane and 60 parts of a 50% solution of thiourea in methylalcohol were mixed at 10 C. The crystalline thiourea-isooctane complex was filtered and washed with normal pentane, then subjected to dry distillation. The complex decomposed, isooctane being distilled while thiourea remained in the still.

EXAMPLE VII Forty parts of an untreated straight run petroleum fraction boiling between 415 F. and 660 F. was treated at 10 C. with 60 parts of a 50% solution of thiourea in methyl alcohol. The crystalline complex of thiourea and hydrocarbons, which formed rapidly, was filtered oil and washed with normal heptane. Water was added to the crystals and the mixture was warmed to about 80 C. The crystals coalesced to form an immiscible layer over the water. After decantation it was found that the upper layer was composed of a mixture of hydrocarbons, while the aqueous layer was a solution of thiourea.

I claim as my invention:

1. A composition of matter comprising a crystalline complex of triptane and thiourea.

2. A composition of matter comprising a crystalline complex of cyclohexane and thiourea.

3. A composition of matter comprising a crystalline complex of methylcyclopentane and thiourea.

4. A composition of matter comprising a crystalline complex of a cycloparaflln hydrocarbon and thiourea.

5. The process which comprises contacting thiourea and a hydrocarbon of the group consisting of isoparaifins, naphthenes, isoolefins,

cycloolefins and alkylated aromatic hydrocarbons having at least one isoparamn radical of at least 6 carbon atoms in the presence of water at a temperature below C. and isolating the complex so formed.

6. The process which comprises contacting thiourea and a hydrocarbon of the group consisting of isoparafl'lns, naphthenes, isoolefins, cycloolefins and alkylated aromatic hydrocarbons having at least one isoparaflin radical of at least 6 carbon atoms in the presence of an alcohol at a temperature below 75 C. and isolating the product so formed.

7. In an extractive fractionation process for separating a mixture of organic compounds at least a fraction of said mixture comprising a hydrocarbon of the group consisting of isoparafiins, naphthenes, isoolefins, cycloolefins and 'alkylated aromatic hydrocarbons having at least one isoparafiln radical of at least 6 carbon atoms, the steps comprising contacting said mixture with thiourea at a temperature below 75 C. to produce twophases, one of said phases comprising complexes of thiourea and a hydrocarbon fraction of said mixture, and separating said phases.

8. As a new composition of matter, a crystalline complex of thiourea with a hydrocarbon of the group consisting of isoparairlns, naphthenes, isoolefins, cycloolefins and alkylated aromatic hydrocarbons having at least one isoparafiin radical of at least 6 carbon atoms.

9. The process which comprises contacting thiourea at a temperature below 75 C. with a mixture of hydrocarbons, said mixture containing as a fraction thereof at least one hydrocarbon of the group consisting of isoparaflins, naphthenes, isoolefins, cycloolefins and alkylated aromatic hydrocarbons having at least one isoparaflin radical of at least 6 carbon atoms, whereby crystalline complexes are formed between thiourea and hydrocarbons from said group.

10. The process for the fractionation of a mixture of petroleum hydrocarbons, said mixture containing as a fraction thereof at least one hydrocarbon of the group of isoparaflins, naphthenes, isoolefins, cycloolefins and alkylated aromatic hydrocarbons having at least one isoparaflin radical of at least 6 carbon atoms, which comprises contacting saidmixture with thiourea at a temperature below 75 C., whereby crystalline complexes are formed between thiourea and hydrocarbons of said group, isolating the complexes and regenerating the hydrocarbons therefrom.

11. A composition of matter comprising a crystalline complex of an isoparaflln hydrocarbon and thiourea.

12. The process which comprises contacting thiourea at a temperature below 50 C. with a mixture of hydrocarbons, said mixture containing as a fraction thereof at least one hydrocarbon oi the group consisting of isoparaflins, naphthenes. isooleiins, cyclooleilns, and alkyiated aromatic hydrocarbons having at least one 180- paraflin radical of at least 6 carbon atoms whereby crystalline complexes are formed between thiourea and hydrocarbons from said group.

13. The process which comprises contacting thiourea and a hydrocarbon of the group consisting oi isoparamns, naphthenes, isooleflns, cyclooieflns and alkylated aromatic hydrocarbons having at least one isoparaflln radical of at least 6 carbon atoms in the presence of a lower monohydric alcohol at a temperature below 75 C. and isolating the product so formed.

14. The process which comprises contacting thiourea and a hydrocarbon of the group consisting of isoparafllns; naphthenes, isooleflns, cyclooleflns and alkylated aromatic hydrocarbons having at least one isoparaflln radical of at least 6 carbon atoms in the presence of aqueous alcohol at a temperature below 75 C. and isolating the product so formed.

24 15. A composition or matter comprising a cry:- talline complex of iso-octane and thiourea.

16. A composition of matter comprising a crystalline complex of 2,3-dimethylbutane and thiourea.

LLOYD C. FETTERLY.

REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS published by Euke, Stuttgart (1927) pages 166-0. McCasland: Jour. Am. Chem. soc., vol. 88, 533

go (1936) i Neuckl: Berichte, vol. 7, 779-780 (1874). Angla: Comptes Rendus, vol. 224, 402-404. 

9. THE PROCESS WHICH COMPRISES CONTAINING THIOUREA AT A TEMPERATURE BELOW 75*C. WITH A MIXTURE OF HYDROCARBONS, SAID MIXTURE CONTAINING AS A FRACTION THEREOF AT LEAST ONE HYDROCARBON OF THE GROUP CONSISTING OF ISOPARAFFINS, NAPHTHENES, ISOOLEFINS, CYCLOOLEFINS AND ALKYLATED AROMATIC HYDROCARBONS HAVING AT LEAST ONE ISOPARAFFIN RADICAL OF AT LEAST 6 CARBON ATOMS, WHEREBY CRYSTALLINE COMPLEXES ARE FORMED BETWEEN THIOUREA AND HYDROCARBONS FROM SAID GROUP. 